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Day 2 > Mass Transfer > Flashcards

Mass Transfer Flashcards

1
Q

The feed to fractionating column is changed from saturated vapour to saturated liquid. If the separation and reflux ratio remains unchanged, the number of ideal stages will

A

increase

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2
Q

With lapse of time, the overhead composition of light component in case of batch distillation with constant reflux

A

decreases

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3
Q

According to the film theory of mass transfer, the mass transfer co-efficient is proportional to (where,D= molecular diffusivity)

A

D

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4
Q

Dry bulb temperature of the gas is __________ the wet bulb temperature.

A

more than

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5
Q

The rough value of diffusion co-efficient of water vapor into air at 25°C may be about __________ cm2/sec.

A

0.25

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6
Q

The recovery of pencillin from the acidified fermentation broth is done by

A

liquid extraction

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7
Q

A binary mixture of benzene and cyclohexane is separated by

A

extractive distillation

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8
Q

Component A is diffusing in a medium B. The flux NA relative to a stationary point is equal to the flux due to molecular difusion, if

A

there is equimolar counter diffusion.

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9
Q

Cox chart is useful in the design of

A

distillation column

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10
Q

Absorption factor, for a fixed degree of absorption from a fixed amount of gas should be

A

> 1

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11
Q

Selectivity of the solvent used in solvent extraction should be

A

> 1

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12
Q

Fine solids can not be leached in a Pachuka tank.

A

Wrongggg

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13
Q

NSc/NPr is called the

A

Lewis number

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14
Q

The film penetration model of mass transfer was enunciated by

A

Toor and Marchello

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15
Q

The most economical range of absorption factor is

A

1.25 to 2

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16
Q

In case of __________ distillation, a solvent is added to alter the relative volatility of the mixture to be separated.

A

extractive

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17
Q

Berl saddle made of carbon cannot be used for

A

oxidising atmosphere

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18
Q

1 kg of a saturated aqueous solution of a highly soluble component A at 60°C is cooled to 25°C. The solubility limits of A are (0.6 kgA/kg water) at 60°C and (0.2 kgA/kg water) at 25°C. The amount in kg of the crystals formed is

A

0.2

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19
Q

The commonly used solvent in supercritical extraction is

A

carbon dioxide

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20
Q

The operating line lies above the equilibrium curve in case of a gas desorber.

A

Wrongggg

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21
Q

A mixture of 10% C6H6 vapour in air at 25°C and 750 mm Hg has a dew point of 20°C. Its dew point at 30°C and 700 mm Hg will be around __________ °C.

A

18.7

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22
Q

If the amount of the steam used in steam distillation is increased, the temperature of distillation

A

decreases

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23
Q

Moisture in a solid exerting an equilibrium vapour pressure equal to that of the pure liquid at the same temperature is called the __________ moisture.

A

unbound

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24
Q

When the psychometric ratio is __________ then the adiabatic saturation temperature and wet bulb temperature becomes equal.

A

1

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25
Q

Desirable value of absorption factor in an absorber is

A

> 1

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26
Q

Sticky material can be dried in a __________ dryer.

A

tray

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27
Q

__________ developed the film theory.

A

Higbie

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28
Q

Which of the following parameters remains almost constant during adiabatic saturation of unsaturated air ?

A

Wet Bulb Temperature

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29
Q

With increase in absolute humidity, the dew point of an unsaturated mixture of air and water vapor (at constant pressure and temperature)

A

increases

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30
Q

Water-ethyl alcohal solution can be concentrated (in respect of alcohal concentration) by __________ distillation.

A

vacuum

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31
Q

Extraction of pencillin employs a __________ extraction coloumn.

A

centrifugal

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32
Q

In case of gases, the binary diffusivity is proportional to (where,P= pressure)

A

1/P

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33
Q

(NSh/NRe.NSc) is termed in mass transfer operation as the

A

Stanton Number

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34
Q

For the same process conditions, the reflux ratio of an unlagged distillation column

A

increases in winter

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35
Q

Acetone is to be removed from air in an isothermal dilute absorber using pure water as solvent. The incoming air contains 5 mole% of acetone (yin= 0.05). The design equation to be used for obtaining the number of trays (N) of the absorber is, N+2 = 6 log (yin/yout).For 98% recovery of acetone, the number of trays required is/are

A

9

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36
Q

Schimdt number and Lewis number for pure air at atmospheric conditions are respectively

A

< 1 and ≈ 1

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37
Q

Diameter of randomly packed tower is normally more than 1.2 metres.

A

Wrongggg

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38
Q

Azeotropism for ethyl alcohol-water system disappears by

A

decreasing pressure

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39
Q

Heat sensitive materials with very high latent heat of vaporisation may be economically separated using

A

liquid extraction

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40
Q

An alkaline solution is used to reduce the concentration of carbon dioxide in a stream from 10% to 0.1% by absorption with irreversible chemical reaction. The overall number of transfer units based on gas phase is

A

4.605

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41
Q

JDfactor for mass transfer is a function of Reynolds number. Mass transfer by molecular diffusion from a single drop to surrounding still air is given by

A

Nsh = 2

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42
Q

Zirconia probe is used for the humidity measurement.

A

Wronggggg

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43
Q

The value ofNA/(NA+NB), for steady state equimolal counter diffusion of two gases ‘A’ and ‘B’ is

A

∞

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44
Q

With increase in the concentration of the adsorbate, the integral heat of adsorption

A

decreases

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45
Q

An air-water vapour mixture has a dry bulb temperature of 60°C and a dew point temperature of 40°C. The total pressure is 101.3 kPa and the vapour pressure of water at 40°C and 60°C are 7.30 kPa and 19.91 kPa respectively.The humidity of air sample expressed as kg of water vapour/kg of dry air is

A

0.152

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46
Q

Nitrobenzene (boiling point = 210.6°C) is steam distilled at 1 atm pressure.Nitrobenzene will distill off __________ °C.

A

< 100

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47
Q

Vanderwall adsorption is also called chemisorption.

A

Wronggggggg

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48
Q

In a moderately sized packed absorption tower, channeling (which is most severe with stacked packings) can be minimised by taking the ratio of tower diameter to packing diameter

A

> 8:1

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49
Q

Penetration model (theory) for mass transfer was enunciated by

A

Higbie

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50
Q

Surface renewal model of mass transfer was enunciated by

A

Danckwerts

51
Q

When the __________ the relative humidity of air decreases, despite an increase in the absolute humidity.

A

temperature rises

52
Q

For turbulent mass transfer in pipes, the Sherwood number depends on the Reynolds number as

A

Re0.83

53
Q

Mass transfer co-efficient ‘K’ according to penetration theory varies with mass dif-fusivity as

A

D0.5

54
Q

During constant rate drying period, vaporisation rate per unit drying surface area

A

does not change with time

55
Q

Mass transfer co-efficient does not account for gase-liquid diffusion.

A

Wrongggg

56
Q

For a fixed number of ideal stages in a distillation column, as the reflux ratio is increased, the difference in composition between the top and bottom product streams

A

increases

57
Q

According to Chilton-Colburn analogy for mass transfer,NSt.NSc2/3is equal to

A

f/2

58
Q

A pure drug is administered as a sphere and as a cube. The amount of drug is the same in the two tablets. Assuming that the shape and size do not influence the mass transfer, the ratio of rate of dissolution in water at t = 0 for the cubic to spherical tablet is

A

1.24

59
Q

Minimum reflux ratio in a distillation column results in

A

maximum condenser size

60
Q

In extraction, as the temperature increases, the area of hetrogeneity (area covered by binodal curve)

A

decreases

61
Q

1 Nm3of dry air is lighter than 1Nm3of humid air.

A

Wrongggg

62
Q

In case of an unsaturated mixture of gas and vapor, the percentage saturation is __________ its relative saturation.

A

lower than

63
Q

At constant pressure, with increase of temperature, the dew point will

A

increase

64
Q

For a single component absorber, the operating line is straight only when plotted in term of __________ units.

A

mole ratio

65
Q

Molecular diffusion in solid is much faster than that in liquids.

A

Wronggggg

66
Q

Laboratory determination of the dif-fusivity of vapor is done by __________ method.

A

Winkel mann’s

67
Q

Unsaturated air (with dry and wet bulb temperatures being 35 and 25°C respectively) is passed through water spray chamber maintained at 35°C. The air will be

A

humidified

68
Q

For absorbing a sparingly soluble gas in a liquid, the

A

liquid side coefficient should be increased.

69
Q

A natural draft cooling tower is filled with wooden grids, which covers about __________ percent of the tower height.

A

10-15

70
Q

The boiling points of pure components of a binary system __________ with increase in total pressure of the system.

A

increases

71
Q

The change in enthalpy, when a unit quantity of gas is absorbed by relatively large quantity of adsorbent (on which a definite concentration of the adsorbed gas already exists) is termed as the

A

differential heat of adsorption.

72
Q

Penetration theory relates the average mass transfer co-efficient (K) with diffusivity (D) as

A

K ∝ √D

73
Q

Rate of adsorption increases as the

A

temperature decreases.

74
Q

At 750°K and 1 atm, the approximate value of Schmidt number for air is

A

0.1

75
Q

The velocity, concentration and temperature boundary, for the boundary layer development on a flat plate during connective mass transfer will be same, if

A

NSc=NPr=NLe

76
Q

Which of the following is used for the concentration of rubber latex ?

A

Agitated film evaporator

77
Q

In a single stage extraction process, 10 kg of pure solventS(containing no solute A) is mixed with 30 kg of feedFcontainingAat a mass fraction xf= 0.2. The mixture splits into an extract phaseEand a raf-finate phaseRcontainingAat xB= 0.5 and xR= 0.05 respectively. The total mass of the extract phase is (in Kg)

A

8.89

78
Q

When the feed to a distillation column is a saturated liquid, slope of the feed line is

A

infinity

79
Q

At the same gas flow rate, the pressure drop in a packed tower being irrigated with liquid __________ that in dry packed tower.

A

greater than

80
Q

With increase in pressure, the relative volatility for a binary system

A

decreases

81
Q

Absorption factor method is used to calculate the number of ideal stages, when

A

both operating and equilibrium lines are parallel.

82
Q

What is the reflux ratio at total reflux ?

A

Infinity

83
Q

In case of a desorber (stripper), the

A

operating line always lies below the equilibrium curve.

84
Q

__________ column is the most suitable for achieving the best performance for mass transfer operations involving liquid with dispersed solids.

A

Plate

85
Q

In case of an absorber, the operating

A

line always lies above the equilibrium curve.

86
Q

The equilibrium moisture content of the solid can be reduced by increasing the absolute humidity.

A

Wrongguee

87
Q

Air at a particular humidity is heated in a furnace. The new dew point

A

increases

88
Q

Henry’s law states that the

A

partial pressure of a component over a solution is proportional to its mole fraction in the liquid.

89
Q

The diffusivity (D) in a binary gas mixture is related to the temperature (T) as

A

D ∝ T^1.5

90
Q

The slope of 9-line is determined by the

A

thermal condition of the feed

91
Q

A distillation column with N plates is being operated under normal conditions. At some point of time, the operation is shifted to total reflux condition (i.e., no product and residue are being withdrawn and feed to the column is stopped). At the new steady state,

A

the top and bottom compositions correspond to the maximum enrichment available.

92
Q

The dew point of an unsaturated gas-vapor mixture does not depend upon the __________ of the mixture.

A

temperature

93
Q

Which one of the following devices is not used for both the absorption as well as the liquid-liquid extraction processes ?

A

Wetted wall columns

94
Q

With increase in solvent rate, the number of transfer units,NtoG, for a fixed degree of absorption from a fixed amount of gas

A

decreases

95
Q

For a binary mixture with low relative volatility, continuous rectification to get pure products will require

A

high reflux ratio

96
Q

The temperature of water cooled in cooling tower is always __________ temperature of entering air.

A

more than the wet bulb

97
Q

Solvent used in extractive distillation

A

changes the relative volatility of the original components.

98
Q

The value ofL/mGratio for economical absorption operation ranges from

A

1.25 to 2.0

99
Q

The operating line always lies below the equilibrium solubility curve in case of a single component stripper.

A

Wrongguee

100
Q

Dryer widely used in a textile industry is __________ dryer.

A

conveyor

101
Q

Steady state equimolal counter diffusion is encountered in

A

separation of a binary mixture by distillation.

102
Q

The capacity of a distillation coloumn is maximum at total reflux.

A

Wrongguee

103
Q

The value ofNA/(NA+NB) for steady state molecular diffusion of gas ‘A’ through non-diffusing gas ‘B’ is

A

1

104
Q

When the mixture to be distilled has a very high boiling point and the product material is heat sensitive, the separation technique to be used is __________ distillation.

A

steam

105
Q

Azeotropic distillation is employed to separate

A

constant boiling mixture

106
Q

The drying time between fixed moisture content within diffusion controlled ‘falling rate period’ is proportional to (assuming that drying occurs from all surfaces of the solid) (where,T= thickness of the solid )

A

T²

107
Q

Pressure drop through plate tower as compared to that through packed tower, for the same duty will be

A

more

108
Q

Humidity chart is useful for the solution of problems concerning condensation, vaporisation and air conditioning. At a given dry bulb temperature, value of humidity obtained from the humidity chart directly, is in terms of __________ humidity.

A

molal

109
Q

In an absorption column, the flooding velocity for random packing is __________ that for stacked/regular packing.

A

smaller

110
Q

The fixed cost of a distillation column at minimum reflux ratio is

A

infinite

111
Q

To get high tray efficiency

A

interfacial surface between liquid and gas phase should be large.

112
Q

An azeotropic mixture is a __________ mixture.

A

constant boiling point

113
Q

Large scale drying of sugar is done in a __________ dryer.

A

rotary

114
Q

Which of the following is the most commonly used leaching solvent in vegetable oil industry ?

A

Hexane

115
Q

Which of the following equipments is not used for gas dispersion ?

A

Spray towers

116
Q

Which of the following remains constant during evaporative cooling process with recirculated water supply ?

A

Wet bulb temperature

117
Q

Solvent used in extractive distillation

A

is of low volatility.

118
Q

The diffusivity,DAB(for componentAdiffusing inB) is equal to the diffusivityDBA(for componentBdiffusing inA) for a binary mixture of

A

ideal gases

119
Q

Mass transfer co-efficient is directly proportional toDAB^0.5, according to __________ theory.

A

Penetration

120
Q

For a non-reacting binary mixture of ideal gases, the partial pressure distribution of both components is linear in the case of steady state equimolal counter-diffusion.

A

Wronguee

121
Q

The surface renewal frequency in Danckwerts’ model of mass transfer is given by (KL: mass transfer co-efficient)

A

sqrt(KL^2 x DA)

122
Q

During dehumidification of unsaturated air wet bulb temperature & partial pressure of vapor are not constant. However, during evaporative cooling process with recirculated water supply, the __________ remains constant.

A

wet bulb temperature

123
Q

For an absorber, both equilibrium and operating line will be straight for

A

dilute solution and isothermal operation.

124
Q

Unsaturated air (with dry bulb and wet bulb temperatures being 45°C and 25°C respectively) is passed through a water spray chamber maintained at 23°C. The air will be cooled and

A

humidified with wet bulb temperature decreasing.

Day 2 (7 decks)

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